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Figure 1. Circulating tumor cells (CTCs) enrichment (A-F) and detection (G-I) technologies. A and B: biological property-based techniques. A: positive selection - CTCs can be positively enriched using anti-epithelial or anti-mesenchymal marker antibody; B: negative selection - CTCs can be negatively enriched by depleting leukocyte using antibody against CD45. C-E: physical property-based techniques. C: filtration - CTCs are filtered using a membrane on the basis of the CTC size; D: chip - CTCs are trapped using microchip on the basis of CTC size and deformability; E: ficoll gradient centrifugation - CTCs are separated through a centrifugation on a ficoll density gradient on the basis of CTC density. F: physical and biological property-based techniques, CTC-chip - firstly, CTCs are selected on the basis of CTCs size, and then CTCs are isolated by magnetic bead-conjugated EpCAM antibodies, while normal hematopoietic cells are depleted by magnetic bead-conjugated antibodies against CD45. G: immunocytologial techniques - CTCs can be detected by using a combination of anti-epithelial, anti-mesenchymal, anti-tissue-specific marker, or anti-tumor-associated antibodies. H: molecular techniques - CTCs can be detected by using RNA-based technologies. I: functional assay - viable CTCs can be isolated by detecting secretion of specific tumor proteins from CTCs. MACS: magnetic activated cell sorting; FACS: fluoroscence-assited cell sorting; FAST: fiber-optic array scanning technology; FISH: fluorescence in situ hybridization; RT-PCR: reverse transcription polymerase chain reaction; EPISPOT: epithelial immunospot; EMT: epithelial mesenchymal transition